1. Field of the Invention
The present invention relates to an optical projection system. More particularly, the present invention relates to an optical projection system having a simplified design.
2. Description of Related Art
Recently, the technology of liquid crystal display (LCD) has been broadly applied in a variety of electronic devices such as liquid crystal television, notebook, desktop computer, or liquid crystal projector. Specially, the liquid crystal projector is developed for displaying large size image. Therefore, the image resolution of the liquid crystal projector is dependent on the liquid crystal panel adopted therein, and generally a high resolution liquid crystal panel is provided.
The liquid crystal panel used in the conventional liquid crystal projector generally includes a liquid crystal display component constructed on a glass substrate or a silicon substrate. In general, the thin film transistor (TFT) or metal oxide semiconductor (MOS) transistor is provided as an active component of the liquid crystal panel. The active component is used to drive the liquid crystal via the pixel electrodes electrically connected thereto for displaying the image. Since the liquid crystal panel that constructed on the glass substrate or the silicon substrate has a small size and high resolution, the size of the liquid crystal projector may be reduced. In general, the performance of the liquid crystal projector is highly dependent on the design of the optical projection system.
Hereinafter, the principle of image projection of a conventional liquid crystal projector will be described. For example, in an optical projection system of a conventional reflecting type liquid crystal projector, a white light is provided by a light source. Then, the white light is separated by a dichroic mirror into red light, which transmits through the dichroic mirror and a light having a mixture of blue and green lights which is reflected by the dichroic mirror. Thereafter, the transmitted red light is separated into an S polarized red light and a P polarized red light by a polarization beam splitter. The S polarized (or P polarized) red light is incident to a red-light liquid crystal panel, which is then reflected and modulated to carry a red image signal. On the other hand, the light having mixture of blue and green lights is separated by a color separation mirror into a green light, which is reflected by the separation mirror and a blue light, which is transmitted through the color separation mirror. The reflected green light is separated into S polarized and P polarized green lights by a polarization beam splitter, and then the S polarized (or P polarized) green light is reflected and modulated by a green-light liquid crystal panel. In the same way, the transmitted blue light is separated into S polarized and P polarized blue light via a polarization beam splitter, and then the S polarized (or P polarized) blue light is reflected and modulated by a blue-light liquid crystal panel. Thereafter, the modulated red, green and blue light having a red, green and blue image signals respectively are incident into an X-cube dichroic prism and are combined therein. Finally, an image is outputted, which can be projected to the screen via a projection lens.
Accordingly, in the conventional optical projection system, a white light is provided by a light source, and then the white light is separated into red light, green light and blue light by dichroic mirrors. Then, the red light, green light and blue light are modulated to carry the red, green and blue image signals via three liquid crystal panels respectively. Finally, these image signals are combined by the X-cube dichroic prism to output an image and projected by the projection lens. However, since the light is separated by dichroic mirrors and combined by dichroic prism, the cost of the projector is high and the design of the light path is complex.